Over recent years, the number of transmission ratios available on bicycle gear change devices has progressively increased and sprocket assemblies for the rear wheel of a bicycle having nine or ten sprockets are increasingly common on the market. The progressive increase in the number of sprockets requires ever increasing research for reducing the weight of the sprocket assembly. In U.S. Pat. No. 5,935,034, assigned to the same assignee as the present invention, a sprocket assembly is described that includes a support member having a radially internal portion shaped such that it couples with a freewheel device and a radially external fastener portion. Two sprockets are mounted on the opposite surfaces of the fastener portion. A third sprocket can be mounted on the support member in addition to the first two sprockets through a plurality of spacer bushings. U.S. Pat. No. 6,102,821 describes a sprocket assembly in which two sprockets are fixed on opposite sides of a sprocket support member by pins that engage with aligned holes of the sprockets and of the support member.
With the progressive increase in the number of sprockets, in addition to the need for reducing the weight of the assembly, there is also the need for arranging the sprockets in positions that are closer one to the other. As a consequence, the space available for the sprocket support member becomes more limited. On the other hand, this support member performs an important structural function and it is necessary to ensure that it has high rigidity and resistance characteristics.